1. Field of the Invention
This invention relates to a process for inducing cytochrome P-450 enzyme production in bacteria of the genus Streptomyces using inducers such as soybean flour, genistein or genistin. Streptomyces enriched in their cytochrome P-450 concentration are useful in carrying out a number of important chemical conversions including the conversion of procarcinogens into mutagens. This invention also relates to a process for determining the mutagenicity of a chemical, using novel bacterial organisms containing both the means to activate promutagens and the means to detect the mutagenic activity of mutagens.
2. Background
Cytochrome P-450 is a term for a group of unique heme proteins which form carbon monoxide complexes with a major absorption band at wavelengths around 450 nm. These proteins are isozymes which carry out oxidase functions in a wide variety of mixed function oxidase systems involved in biosynthesis and catabolism of specific cell or body components, and in the metabolism of foreign substances entering organisms. Oxygenating enzymes such as P-450 appear to be fundamental cellular constituents in most forms of aerobic organisms. The activation of molecular oxygen and incorporation of one of its atoms into organic compounds catalyzed by these enzymes are reactions of vital importance not only for biosynthesis and degradation of steroid hormones necessary for sustaining life, but also for metabolic activation or inactivation of foreign agents such as drugs, food preservatives and additives, insecticides, carcinogens and environmental pollutants.
It is an object of the present invention to provide a process for the production of cytochrome P-450 enzymes which utilizes bacteria from the genus Streptomyces and a soybean derivative such as soybean flour, or the isoflavonoids genistin or genistein. One of the surprising aspects of the invention is that the Streptomyces cytochrome P-450 enzymes are induced, not by a known substrate, but by certain soybean derivatives. It is also an object of the present invention to provide bacteria enriched in cytochrome P-450 which are useful in carrying out mutagenicity assays. The P-450 enzymes in such enriched bacteria bear a resemblance, in their oxidative reactions, to the cytochrome P-450 enzymes of mammalian liver and thus may serve as an economical and convenient source of cytochrome P-450 for use in a modified version of an Ames-type Salmonella assay for carcinogenicity and mutagenicity. Although cytochrome P-450 isozymes are found in a wide variety of organisms and tissues, they vary greatly in their composition and functions they can perform. Thus, it is suprising that the cytochrome P-450 enzymes of Streptomyces carry out a spectrum of oxidative reactions that are sufficiently similar to those carried out by the cytochrome P-450 enzymes of the mammalian liver that they may serve as a substitute in the Ames test.
It is a further object of the present invention to develop a process to detect the mutagenic activity of chemicals using novel, genetically engineered Streptomyces organisms and a single incubation of said organisms with suspected carcinogenic chemicals, thus greatly simplifying the screening of chemicals for mutagenic activity. Furthermore, the process of this invention obviates the use of mammalian liver extracts for the conversion of promutagens to mutagens. These and other objects and advantages of the present invention will become apparent hereinafter.